1. Field of the Invention
The present invention relates to brachytherapy devices, and more particularly to a method and assembly for containing the radioisotopes or other radioactive materials utilized in brachytherapy devices.
2. Discussion of the Related Art
Percutaneous transluminal coronary angioplasty (PTCA) is a therapeutic medical procedure used to increase blood flow through an artery and is the predominant treatment for coronary vessel stenosis. The increasing popularity of the PTCA procedure is attributable to its relatively high success rate and its minimal invasiveness compared with coronary by-pass surgery. Patients treated utilizing PTCA; however, may suffer from restenosis. Restenosis refers to the re-narrowing of an artery after a successful angioplasty procedure. Restenosis usually occurs within the initial six months after an angioplasty. Early attempts to alleviate the effect of restenosis included repeat PTCA procedures or by-pass surgery, with attendant high cost and added patient risk.
More recent attempts to prevent restenosis by use of drugs, mechanical devices, and other experimental procedures have limited long term success. Stents, for example, dramatically reduce acute reclosure and slow the effects of smooth muscle cell proliferation by enlarging the maximal luminal diameter, but otherwise do nothing substantial to slow the proliferative response to the angioplasty induced injury.
Restenosis is now believed to occur at least in part as a result of injury to the arterial wall during the lumen opening angioplasty procedure. In some patients, the injury initiates a repair response that is characterized by hyperplastic growth of the vascular smooth muscle cells in the region traumatized by the angioplasty. Intimal hyperplasia or smooth muscle cell proliferation narrows the lumen that was opened by the angioplasty, regardless of the presence of a stent, thereby necessitating a repeat PTCA or use of other procedures to alleviate the restenosis.
Recent studies indicate that intravascular radiotherapy (IRT) has promise in the prevention or long-term control of restenosis following angioplasty. Intravascular radiotherapy may also be used to prevent or delay stenosis following cardiovascular graft procedures or other trauma to the vessel wall. Proper control of the radiation dosage, however, appears to be important to inhibit or substantially arrest hyperplasia without causing excessive damage to healthy tissue. Underdosing will result in inadequate inhibition of smooth muscle cell hyperplasia, or possibly even exacerbation of hyperplasia and resulting restenosis.
Radiation therapy may also be utilized in the treatment of other diseases such as cancerous and non-cancerous tumors or other proliferative normal tissue disorders. In this type of therapy, the ultimate aim is to destroy the malignant tissue without causing excessive radiation damage to nearby healthy, and possibly vital tissue. This is difficult to accomplish because of the proximity of malignant tissue to healthy tissue.
Brachytherapy is a form of radiation treatment in which an ionizing radiation source, for example, an intravascular radiotherapy source ribbon, is placed into or adjacent to a tumor or stenotic lesion. Although any number of radioactive substances and/or radioactive sources may be utilized in brachytherapy, Iodine-125 is currently a good candidate isotope for vascular brachytherapy. Iodine-125 has been used as a liquid or immobilized onto a variety of surfaces for diagnostic and therapeutic purposes. It has already been fashioned into a variety of shapes and used clinically for cancer treatment as briefly described above. One standard method for immobilizing Iodine-125 on to a solid surface is through electroplating. Currently, Iodine-125 is immobilized onto the surface of solid silver wires for a very secure bond. Silver is specifically utilized because of the extremely secure bond it forms with the Iodine-125; however, impurities and the like may cause the Iodine-125 to xe2x80x9cbreak freexe2x80x9d from the silver regardless of how strong the bond and potentially create a contamination problem.
The method and assembly for containing radioactive materials of the present invention provides a means for overcoming the difficulties associated with the devices currently in use as briefly described above.
In accordance with one aspect, the present invention is directed to a method for containment of radioactive substances in an intravascular radiotherapy source ribbon assembly. The method comprises positioning a radioactive substance absorber in proximity to a radioactive source core; and sealing the radioactive substance absorber and radioactive source core in a radiation transparent container.
In accordance with another aspect, the present invention is directed to an intravascular radiotherapy source ribbon assembly. The assembly comprises a sealed, elongated flexible tube defining an interior cavity, a radioactive source core disposed within the interior cavity, and a radioactive substance absorber disposed in proximity to the source core to absorb stray radioactive matter.
The method and assembly for containing radioactive materials of the present invention comprises utilizing carbon in any number of forms and any number of configurations as a means for absorbing free radioactive materials. A typical intravascular radiotherapy source ribbon comprises a source core disposed within a radio-transmissive, sealed container. It is possible that particles, salts or gaseous forms of the radioactive substance comprising the core may break free from the core and migrate through the outer components of the ribbon. The incorporation of carbon fiber, or the like, in the wall of the container, or as a layer adjacent to the source, would serve as a radioactive substance absorber as well as strengthen the polymer. As the radioactive material contamination permeates the assembly, the carbon would serve as an absorption point and slow the transmission of contaminants to the surface by bonding them to the carbon through absorption. Since the radioactive substance is slowed prior to reaching the surface, the chance of spreading the contaminants is substantially reduced. This technique could be thought of as a xe2x80x9cbelt and suspendersxe2x80x9d approach to improve the radiation safety of any radioactive liquid or gas based radiotherapy device.